[PATCH 4/5] tick/broadcast: Program wakeup timer when entering idle if required

[Will Deacon]

When configuring the broadcast timer on entry to and exit from deep idle
states, prefer a per-CPU wakeup timer if one exists.

On entry to idle, stop the tick device and transfer the next event into
the oneshot wakeup device, which will serve as the wakeup from idle. To
avoid the overhead of additional hardware accesses on exit from idle,
leave the timer armed and treat the inevitable interrupt as a (possibly
spurious) tick event.

Cc: Frederic Weisbecker <fweisbec at gmail.com>
Cc: Thomas Gleixner <tglx at linutronix.de>
Cc: Marc Zyngier <maz at kernel.org>
Cc: Lorenzo Colitti <lorenzo at google.com>
Cc: John Stultz <john.stultz at linaro.org>
Cc: Stephen Boyd <sboyd at kernel.org>
Signed-off-by: Will Deacon <will at kernel.org>
---
 kernel/time/tick-broadcast.c | 38 +++++++++++++++++++++++++++++++++++-
 1 file changed, 37 insertions(+), 1 deletion(-)

diff --git a/kernel/time/tick-broadcast.c b/kernel/time/tick-broadcast.c
index 8bd8cd69c8c9..ba5264e210d9 100644
--- a/kernel/time/tick-broadcast.c
+++ b/kernel/time/tick-broadcast.c
@@ -96,6 +96,15 @@ static struct clock_event_device *tick_get_oneshot_wakeup_device(int cpu)
 	return per_cpu(tick_oneshot_wakeup_device, cpu);
 }
 
+static void tick_oneshot_wakeup_handler(struct clock_event_device *wd)
+{
+	/*
+	 * If we woke up early and the tick was reprogrammed in the
+	 * meantime then this may be spurious but harmless.
+	 */
+	tick_receive_broadcast();
+}
+
 static bool tick_set_oneshot_wakeup_device(struct clock_event_device *newdev,
 					   int cpu)
 {
@@ -116,6 +125,7 @@ static bool tick_set_oneshot_wakeup_device(struct clock_event_device *newdev,
 	if (curdev && newdev->rating <= curdev->rating)
 		return false;
 
+	newdev->event_handler = tick_oneshot_wakeup_handler;
 set_device:
 	per_cpu(tick_oneshot_wakeup_device, cpu) = newdev;
 	return true;
@@ -903,16 +913,42 @@ static int ___tick_broadcast_oneshot_control(enum tick_broadcast_state state,
 	return ret;
 }
 
+static int tick_oneshot_wakeup_control(enum tick_broadcast_state state,
+				       struct tick_device *td,
+				       int cpu)
+{
+	struct clock_event_device *dev, *wd;
+
+	dev = td->evtdev;
+	if (td->mode != TICKDEV_MODE_ONESHOT)
+		return -EINVAL;
+
+	wd = tick_get_oneshot_wakeup_device(cpu);
+	if (!wd)
+		return -ENODEV;
+
+	if (state == TICK_BROADCAST_ENTER) {
+		clockevents_switch_state(dev, CLOCK_EVT_STATE_ONESHOT_STOPPED);
+		clockevents_switch_state(wd, CLOCK_EVT_STATE_ONESHOT);
+		clockevents_program_event(wd, dev->next_event, 1);
+	}
+
+	return 0;
+}
+
 int __tick_broadcast_oneshot_control(enum tick_broadcast_state state)
 {
 	struct tick_device *td = this_cpu_ptr(&tick_cpu_device);
 	int cpu = smp_processor_id();
 
+	if (!tick_oneshot_wakeup_control(state, td, cpu))
+		return 0;
+
 	if (tick_broadcast_device.evtdev)
 		return ___tick_broadcast_oneshot_control(state, td, cpu);
 
 	/*
-	 * If there is no broadcast device, tell the caller not
+	 * If there is no broadcast or wakeup device, tell the caller not
 	 * to go into deep idle.
 	 */
 	return -EBUSY;
-- 
2.31.1.818.g46aad6cb9e-goog